1. Field of the Invention
The present invention relates to a wired circuit board to connect with a suspension board with circuit equipped with a magnetic head of a hard disk drive.
2. Description of the Prior Art
In the hard disk drive, the suspension board with circuit equipped with the magnetic head has read lines and write lines for transmitting read signals and write signals to the magnetic head. The read lines and the write lines are connected to terminal portions of the wired circuit board equipped with an electronic device such as a preamplifier integrated circuit (IC). The read signals from the read lines and the write signals from the write lines are amplified by the electronic device such as the preamplifier IC placed on the wired circuit board and then transmitted from the wired circuit board to a control circuit board for controlling the magnetic head.
Meanwhile, along with improvement in recent years to fine pitch wiring and to high frequency signal, it is increasingly becoming necessary to control characteristic impedances at connection points between the read lines and write lines of the suspension board with circuit and the terminal portions of the wired circuit board connected thereto.
If there is inconsistency in characteristic impedance at the connection points, transmission efficiency of the signal will be reduced. Particularly, the signal before input to the preamplifier IC (the signal before it is amplified) is so weak that it is easily affected by the characteristic impedance at the connection points, so that the transmission efficiency of the signal is reduced easily.
For example, U.S. Pat. No. 5,712,749 proposes improvement of this suspension board with circuit, according to which an opening is formed in the stainless board at a location under the wires, to optimize the capacitance of the signal, so as to control the characteristic impedance. This proposed construction can control the characteristic impedance of the suspension board with circuit itself, but it cannot control the characteristic impedances at the connection points between the read wire and write wire of the suspension board with circuit and the terminal portions of the wired circuit board connected thereto. Accordingly, the problem of the reduction in transmission efficiency at the connection points remains unavoidable.
The terminal portions, in particular, which are in the form of connection pads, are usually formed to be larger in width than the wires. Due to this, the capacitance is increased at the terminal portions, so that the characteristic impedance is rendered discrete thereat, to cause reflection of the signal. Thus, it is increasingly becoming important to control the characteristic impedance at the connection points.